/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.iotdb.db.mpp.execution.operator.process;

import com.google.common.util.concurrent.ListenableFuture;
import org.apache.iotdb.db.mpp.execution.operator.Operator;
import org.apache.iotdb.db.mpp.execution.operator.OperatorContext;
import org.apache.iotdb.tsfile.read.common.block.TsBlock;

import static com.google.common.base.Preconditions.checkArgument;
import static java.util.Objects.requireNonNull;

public class LimitOperator implements ProcessOperator {

    private final OperatorContext operatorContext;
    private long remainingLimit;
    private final Operator child;

    public LimitOperator(OperatorContext operatorContext, long limit, Operator child) {
        this.operatorContext = requireNonNull(operatorContext, "operatorContext is null");
        checkArgument(limit >= 0, "limit must be at least zero");
        this.remainingLimit = limit;
        this.child = requireNonNull(child, "child operator is null");
    }

    @Override
    public OperatorContext getOperatorContext() {
        return operatorContext;
    }

    @Override
    public ListenableFuture<?> isBlocked() {
        return child.isBlocked();
    }

    @Override
    public TsBlock next() {
        TsBlock block = child.nextWithTimer();
        if (block == null) {
            return null;
        }
        TsBlock res = block;
        if (block.getPositionCount() <= remainingLimit) {
            remainingLimit -= block.getPositionCount();
        } else {
            res = block.getRegion(0, (int) remainingLimit);
            remainingLimit = 0;
        }
        return res;
    }

    @Override
    public boolean hasNext() {
        return remainingLimit > 0 && child.hasNextWithTimer();
    }

    @Override
    public void close() throws Exception {
        child.close();
    }

    @Override
    public boolean isFinished() {
        return remainingLimit == 0 || child.isFinished();
    }

    @Override
    public long calculateMaxPeekMemory() {
        return child.calculateMaxPeekMemory();
    }

    @Override
    public long calculateMaxReturnSize() {
        return child.calculateMaxReturnSize();
    }

    @Override
    public long calculateRetainedSizeAfterCallingNext() {
        return child.calculateRetainedSizeAfterCallingNext();
    }
}
